Heme synthesis in the bone marrow of rats with an acute myelogenous leukemia (Shay Chloroleukemia) is substantially reduced in the early as well as the later stages of the disease suggesting that mechanisms other than encroachment by leukemic elements on the hematopoietic compartment are operating to reduce erythrocytopoiesis. The decline in bone marrow erythropoiesis is observed concomitantly with increases in splenic red blood cell production as noted histologically and by elevations in heme synthesis. The proposed studies are designed to determine: (1) the responsivity of leukemic bone marrow and spleen cultures to erythropoietin as measured by the effect of the hormone on radioiron incorporation into heme, labeled nucleotide incorporation into RNA: (2) the numbers of erythroid precursor (ECFU) elements in leukemic bone marrow and spleen: (3) changes in ALA-Synthetase activity of leukemic hematopoietic tissues: and (4) the effect of leukemic cell products on heme synthesis by normal bone marrow cell suspensions. It is hoped that this multifaceted approach will help elucidate the alterations in the physiological controls on erythropoiesis operative during the leukemic state and in this way, gain some insight into the mechanisms of anemia associated with human granulocytic leukemias.